Pressurized gas cylinders are used to supply gas for numerous commercial, industrial and consumer applications. With a single cylinder connected to supply gas, when the cylinder is empty the supply of gas must be temporary stopped until the cylinder can be replaced. This can lead to lost productivity while the cylinder is being changed.
To overcome this problem, devices have been proposed which allow more than one cylinder to be connected to a switchover manifold which automatically switches the flow of gas to a backup cylinder when the pressure of a cylinder drops below a switchover threshold.
One example of an automatic switchover device is shown and described in U.S. Pat. No. 5,014,733 to Wilson (“Wilson”), which is incorporated by reference herein. In the device described by Wilson, two cylinders are each connected to supply gas pressure to a spool. Each spool acts as a pressure-sensitive valve that is biased to an open position by a spring. Pressurized gas from a first cylinder is directed in sequence through a first spool in the open position to an end chamber of a second spool causing it to close, thereby shutting off the flow from the second cylinder. When the pressure in the first cylinder drops below a predetermined level, the second spool is allowed to move into the open position by the drop in pressure at its end chamber. This allows gas to flow from the second cylinder through the second spool into an end chamber of the first spool, causing it to move into the closed position, thereby shutting off the flow from the first cylinder and permitted it to be disconnected and replaced. A flow separator spool is provided at the outlet of the device to serve as a check valve.